• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.12
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• pp.3360-3371
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• 1995

Hydrodynamic characteristics of a stratified flow at a Y-junction were examined analytically. Gas is supplied through the main horizontal channel and liquid is introduced into the gas stream from the Y-shaped bottom branch. Analysis was performed with irrational flow and inviscid fluid assumptions. The Stokes' inverse transformation technique was adopted to convert the real x-y plane into the x-.psi. plane. The potential flow equation was solved numerically in the transformed (x-.psi.) plane and the interface profile, pressure distribution and the streamlines were obtained. The effects of the inlet conditions, injection angle and the gravity on the flow characteristics were also examined. To check the validity of the present method, the previous resultant the two-dimensional obtuse wedge flow was compared. The inverse transformation technique turned out to be also very useful to predict the hydrodynamic characteristics of a stratified flow with the pressure variation at a Y-shaped mixing junction.

• Journal of the Korean Society of Visualization
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• v.19 no.2
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• pp.63-73
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• 2021

It is essential to accurately predict the change in water level, velocity, and flow rate for each passage of the grit chamber according to the operating conditions of the pump. In this study, VOF multiphase flow analysis was performed, and the flow characteristics of the grit chamber were predicted. As a result of simulations, the sedimentation phenomenon after the entrance of the grit chamber channel is expected to occur on the side walls. When 6 channels are used, the average speed of the channels is about 52% of the design standard, and when 4 channels are used, the value increases to 74% of the design standard. The average water level in the channels tends to decrease as the flow velocity increases, and the water level in the absorption well with a larger flow rate is maintained lower than that in the absorption well with a smaller flow rate.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.4
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• pp.354-361
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• 2008

Cold rolled steel sheet for automotive was treated by Ar/$O_2$ atmospheric pressure plasma to improve the adhesive bonding strength. Through the contact angle test and calculation of surface free energy for cold rolled steel sheet, the changes of surface properties were investigated before and after plasma treatment. The contact angle was decreased and surface free energy was increased after plasma treatment. And the change of surface roughness and morphology were observed by AFM(Atomic Force Microscope). The surface roughness of steel sheet was slightly changed. Based on Taguchi method, single lap shear test was performed to investigate the effect of experimental parameter such as plasma power, treatment time and flow rate of $O_2$ gas. Results shows that the bonding strength of steel sheet treated in Ar/$O_2$ atmospheric pressure plasma was improved about 20% compared with untreated sheet.

• 한국전산유체공학회:학술대회논문집
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• 1995.10a
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• pp.43-48
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• 1995

A numerical computation is carried out to analyse characteristics of flow fields around Air Supported Ships having arbitrary form. The computations are performed in a rectangular grid system with MAC(Marker And Cell) method. The governing equations are represented in a Finite Difference form by forward differencing in time and centered differencing in space except for convection terms. For validation of this numerical analysis method, the computation of flow fields around Catamaran and ACV(Air Cushion Vehicle) with pressure distribution on free surface are done, and that around Surface Effect Ship is also carried out. The results of the computations are compared with the those of existed numerical computation and experimental results with the same condition.

• Journal of Welding and Joining
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• v.20 no.4
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• pp.484-490
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• 2002

The formation and stability of stationary laser weld keyholes were investigated using a numerical simulation. The effect of multiple reflections in the keyhole was estimated using the ray tracing method, and the free surface profile, flow velocity and temperature distribution were calculated numerically. In the simulation, the keyhole was formed by the displacement of the melt induced by evaporation recoil pressure, while surface tension and hydrostatic pressure opposed cavity formation. A transition mode having the geometry of the conduction mode with keyhole formation occurred between the conduction and keyhole modes. At laser powers of 500W and greater, the protrusion occurred on the keyhole wall, which resulted in keyhole collapse and void formation at the bottom. Initiation of the protrusion was caused mainly by collision of upward and downward flows due to the pressure components, and Marangoni flow had minor effects on the flow patterns and keyhole stability.bility.

• 한국가시화정보학회:학술대회논문집
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• 2002.11a
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• pp.81-84
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• 2002

Dispersion of coolant jets in a film cooling flow field is the result of a highly complex interaction between the film cooling jets and the mainstream. In order to investigate the effect of blowing ratios on the film cooling of turbine blade, cylindrical body model was used. Mainstream Reynolds number based on the cylinder diameter was $7.1\;\times\;10^4$. The free-stream turbulence intensity kept at $5.0\%$ by using turbulence grid. The effect of coolant flow rates was studied for blowing ratios of 0.9, 1.3 and 1.6, respectively. The temperature distribution of the cylindrical model surface is visualized by infrared thermography (IRT). Results show that the film-cooling performance may be significantly improved by controlling the blowing ratio. As blowing ratio increases, the adiabatic film cooling effectiveness is more broadly distributed and the area protected by coolant increases. The mass flow rate of the coolant through the first-row holes is less than that through the second-row holes due to the pressure variation around the cylinder surface.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.263-270
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• 1997

For a cylinder in a uniform flow stream, sound is generated by the fluctuating pressure on the cylinder surface due to the vortex shedding behind the cylinder. It is known that the major parameters to predict the sound pressure are the characteristic length of the flow along the cylinder axis and the fluctuating lift coefficient. These parameters strongly depend on the Reynolds number and the yaw angle of the cylinder to the free stream. In this experimental study the effects of yaw on the flow parameters, and consequently on the generated sound are investigated. The surface pressure and the radiated sound are measured simultaneously for different yaw angles and showed that the reduced normal velocity component to the cylinder axis reduces the unsteady lift fluctuation which results in lowered sound press-are level, However, experimental result shows that "the cosine law" which uses the normal velocity component as a characteristic velocity for noise Generation from a yawed cylinder needs to be carefully reviewed. reviewed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.4
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• pp.329-335
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• 2014

This study aimed to understand the internal flow characteristics of a liquid droplet subject to periodic forced vibration. In order to predict the resonance frequency of a droplet, a high-speed camera and macro lens were used to capture internal flow characteristics of a droplet placed on a vibrating hydrophobic surface. Results showed that the droplet assumed a variety of shapes depending on the resonance mode of free droplet, particularly in modes 2, 4, 6, and 8. In addition, the induced internal vortex flow inside the droplet was also observed in each mode. Typically, the induced flow moved upwards along the axis of symmetry and downwards along the surface of the droplet, that is, from the apex to the contact line in modes 2 and 4, after which it broke into a smaller vortex. On the other hand, the large-scale vortex always remained steady in modes 6 and 8. The speed of the flow in mode 4 was always greater than that in mode 2, but those in modes 6 and 8 were similar.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.532-537
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• 2007

Nano imprint lithography(NIL) is a cost-efficient, high-throughput processing technique to transfer nano-scale patterns onto thin polymer films. Polymers used as the resist include UV cured resins as well as thermoplastics such as polymethyl-methacrylate(PMMA). In this study, an analytic investigation was performed for the NIL process of transferring nano scale patterns onto polymeric films. Process optimization calls for a thorough understanding of resist flow during the process. We carried out 2D and 3D numerical analyses of resist flow during NIL process. The simulation incorporated continuum-hypothesis and the effects of surface tension were taken into account. For a more effective prediction of free surface, fixed grid scheme with the volume of fluid (VOF) method were used. The simulation results were verified with experimental results qualitatively. And the parametric study was performed for various process conditions.

• Journal of Biosystems Engineering
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• v.30 no.4 s.111
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• pp.195-201
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• 2005

The output of Stirling engine is influenced by the regenerator effectiveness. The regenerator effectiveness is influenced by heat transfer and flow friction loss of the regenerator matrix. In this paper, in order to provide a basic data for the design of regenerator matrix, characteristics of heat transfer and flow friction loss were investigated by a packed method of matrix in the oscillating flow as the same condition of operation in a Stirling engine. As matrices, several kinds of combined wire screen meshes were used. The results are summarized as follows; The packed meshes with high mesh no. in the side of heater part of regenerator showed effective than the packed meshes with low mesh no. in the side of cooler part of regenerator. The temperature difference and pressure drop of the regenerator were not made by the specific surface area of wire screen meshes but by the minimum free-flow area to the total frontal area. Among the No. 150 single screen meshes, 200-60 combined meshes, the 200-150-100 combined meshes showed the highest in effectiveness.